EP0222627A1 - Device for detecting the imminent depletion of the gas in a liquefied-gas container, and gas lighter equipped with such a device - Google Patents

Abstract

PCT No. PCT/FR86/00300 Sec. 371 Date May 6, 1987 Sec. 102(e) Date May 6, 1987 PCT Filed Sep. 10, 1986 PCT Pub. No. WO87/01801 PCT Pub. Date Mar. 26, 1987.The subject of the invention is a device for the detection of imminent gas depletion of a liquified gas tank, comprising a bundle of fiber optics (22), one end of which, forming an observation surface is visible from the outside of the tank, and other end of which, placed inside of the tank, is in optical contact with a flat surface of a transparent element (20), comprising, on its opposite surface, at least one dioptricelement (26). According to the invention, the lateral walls of the element (26) form with said surface an angle, preferably obtuse, the dimensions of which are such that it is capable, as long as there is liquid gas remaining in the reservoir, of being covered, almost totally, by a mensicus formed of a liquid gas condensate, which thus prevents any total reflection on said surface, of the rays directed by the fiber beams.

Description

The present invention relates to a device capable of detecting the impending exhaustion of gas in a liquefied gas tank. It also relates to a refillable gas lighter equipped with this device.

In its French patent application No. 2 524 980, the Applicant has described a device for detecting a level of liquid in a reservoir, this device comprising a transparent element, one end of which disposed in said reservoir substantially at the level to be detected has a refractive index such that the light rays which propagate there are refracted at the interface, when this end is immersed in the liquid, and are reflected by total reflection, otherwise. In this device, the transparent element consists of a bundle of optical fibers, and the end disposed substantially at the level to be detected consists of a transparent body, one flat face of which is applied against a first end of said bundle of fibers and the other faces of which are such that the incident rays transmitted by the beam can undergo therein at least total reflection and be transmitted in the opposite direction by this beam to its second end when the transparent body is not immersed. The second end of the fiber bundle is fixed to one of the walls of the tank, visible from the outside, or inside the tank.

Such a device can in particular be used with advantage in a gas lighter, to find out if the level of the liquefied gas in the tank has dropped below a certain threshold. However, it does not make it possible to determine with sufficient precision from when there remains in the tank only a quantity of gas corresponding to a few ignitions of the lighter, ten for example, so as to inform the user of the impending exhaustion of the gas, so that it can refill its lighter.

The present invention aims to remedy this drawback by perfecting the device patented previously so that it makes it possible to detect the imminence of the exhaustion of gas in the tank.

The invention is based on the known fact that, when a container contains a liquefied gas, the walls of the container are covered, by a phenomenon of condensation, with a thin film of gas in the liquid phase, so that, in the parts forming a re-entrant angle, a meniscus of liquid tends to form.

If, inside the tank, the external face of the transparent body of the device of the prior art has a re-entrant angle, the path of the incident light rays, moving parallel to the bundle of fibers, will be modified by the presence of the layer of liquid in this angle. Indeed, instead of undergoing a total reflection on this face, as would be the case in the absence of liquefied gas outside, the corresponding light rays will pass through this face, will penetrate into the meniscus of liquid gas, s 'will refract there to come out and lose it inside the tank.

On the observation face of the bundle of optical fibers (end of the bundle disposed outside the tank), the area corresponding to these rays and therefore to the meniscus of liquefied gas will therefore be dark. It will remain so as long as there the liquid gas in the tank and it will become clear that when the liquid _phase ispa- raîtra, which will provide for the user an impending end of signal gas and will indicate that ''it's time to refill the tank with your lighter.

According to the invention, the observation face located at the outer end of the reservoir of the fiber optic bundle will therefore comprise at least one zone which will only become clear when the reservoir is empty of gas in the liquid phase.

The invention therefore relates to a device for detecting the imminence of the exhaustion of gas from a liquefied gas tank, comprising a bundle of optical fibers, one end of which constitutes a observation face, is visible from the outside of the tank, and the other end of which, arranged inside the tank, is in optical contact with a flat face of a transparent element, comprising, on its opposite face, at least one dioptric element whose side walls form an angle, preferably obtuse, with said face and whose dimensions are such that it is suitable, as long as there remains liquid gas in the reservoir, to be covered, substantially in its entirety, by a meniscus formed of a condensate of liquid gas, which thus avoids any total reflection, on said face, of the rays conveyed by the bundle of fibers.

The transparent body may naturally have any desired shape depending on the shape of the desired optical signal, the appearance of which will indicate to the observer the imminent exhaustion of gas in the reservoir.

• La figure 1 illustre la formation d'un ménisque de gaz liquéfié dans un angle d'un corps transparent.
• La figure 2 illustre le phénomène de double réfraction des rayons lumineux résultant de la présence de ce ménisque.
• La figure 3 illustre, en perspective, une forme de mise en oeuvre de l'invention ;
• La figure 4 est une coupe de détail à plus grande échelle de cette forme de réalisation ;
• Les figures 5, 6 et 7 illustrent différentes positions de ce dispositif par rapport au fond d'un résorvoir contonant un gaz liquéfié, et les figures 5', 6' et 7' représentent les signaux correspondants, apparaissant sur la face d'observation du faisceau de fibres optiques.
• Les figures 8 et 9 sont des vues schématiques en perspective, illustrant différentes formes de mise en oeuvre de l'invention.

The accompanying drawings illustrate the invention in principle and in certain embodiments. In these drawings:

• Figure 1 illustrates the formation of a meniscus of liquefied gas in a corner of a transparent body.
• Figure 2 illustrates the phenomenon of double refraction of light rays resulting from the presence of this meniscus.
• FIG. 3 illustrates, in perspective, a form of implementation of the invention;
• Figure 4 is a detail section on a larger scale of this embodiment;
• Figures 5, 6 and 7 illustrate different positions of this device relative to the bottom of a tank containing a liquefied gas, and Figures 5 ', 6' and 7 'show the corresponding signals, appearing on the observation face of the optical fiber bundle.
• Figures 8 and 9 are schematic perspective views illustrating different forms of implementation of the invention.

FIG. 1 shows the meniscus 1 of liquid gas which forms on a transparent body 2 having two connection surfaces 3 and 4 forming an angle α (here an obtuse angle of approximately 135 °), when this transparent body is placed in a enclosure containing gas in liquid phase.

As seen in Figure 2, which is an enlarged view of the connecting portion of the surfaces 3 and 4, the presence of the meniscus 1 changes the path of the light rays 5 which propagate in the transparent body. Indeed, instead of being reflected on the face 4 of this body, by total reflection, on the diopter "transparent material-gas phase", the rays 5 arriving at an angle of incidence i on the face 4 penetrate into the meniscus of liquefied gas 1 by being deflected at an angle of refraction r. They then meet, at an angle of incidence i ', the "liquid phase-gas phase" diopter, on which they refract at an angle r', to then get lost in the interior of the tank.

Indeed, the index of a solid material transparent with respect to the air is generally in a range of _1, 4 to 1.6 methyl methacrylate sold under the appellation PLEXIGLAS, e.g., has an index compared to air or to the gas phase, 1.49, while the refractive index of butane is 1.35 and that of propane 1.29. The total reflection angle A corresponding to various diopters will be of which the following:

As shown in FIG. 2, if the "plexiglass - liquid gas" diopter formed on the face 4 of the transparent body 2 is inclined at 45 ⁰ relative to the axis of the beam of optical fibers, the angle of incidence i (45 °) is less than the angle λ limit for the interface "plexiglas- butane or propane liquid" (respectively 65 ° and 60 ⁰⁾ .It is therefore no total reflection, but refraction.

It will be noted that, if the meniscus of liquid gas 1 did not exist, the angle of incidence i (45 °) would be greater than the limit angle for the interface "plexiglas-butane" or "plexiglas-propane gas "(≃ 42 ⁰ ) and there would then be total reflection.

The rays then meet the second diopter ("butane or liquid propane - butane or propane gas") at an incidence i '. There will also be no total reflection, because, according to the position of the light rays, taking into account the concavity of this second diopter, all the incident rays i 'will be less than 45 ° (this _' te last value being reached, in theory, at the point of tangency of the meniscus 1 with the face 4) and will therefore in all cases be less than the limit angle λ (whose value for the interface "liquid butane-gaseous butane" is 47.7 ° and for the "liquid propane-gaseous propane" interface is 50.8 °).

It is thus clear that the presence of the liquid meniscus 1 causes refraction of the incident rays 5, which will therefore result in a dark area on the observation face formed by the end of the bundle of fibers located outside the lighter.

• - tant que le corps transparent baignera dans la phase liquide, tous les rayons lumineux incidents amenés à celui-ci par le faisceau de fibres optiques pénétreront dans le gaz liquéfié et aucun signal lumineux n'apparaîtra sur la face d'observation du faisceau de fibres, où l'on ne distinguera qu'une tache sombre
• - lorsque le dioptre ne baignera plus dans la phase liquide, mais qu'il subsistera encore du gaz sous phase liquide dans le réservoir, les rayons lumineux incidents seront réfléchis par la ou les faces du corps transparent en contact avec la phase gazeuse, mais non les rayons qui rencontreront le ou les ménisques de phase liquide formés dans les angles du corps transparent ; l'observateur notera donc l'apparition d'un signal lumineux d'une forme déterminée correspondant à celle du corps transparent, entourée d'une ou de zone (s) sombre (s), correspondant au (x) ménisque (s) liquide (s);
• - lorsque le réservoir ne contiendra pratiquement plus de gaz liquéfié, mais essentiellement une phase gazeuse, les zones sombres entourant le signal lumineux disparaîtront et seront remplacées par des zones claires informant ainsi l'observateur qu'il est temps de remplir le réservoir.

Consequently, if the transparent body and the bundle of optical fibers with one end of which it is in optical contact are housed in a tank of liquefied gas, a user, by examining the observation face of the bundle of fibers will be able to note that:

• - as long as the transparent body is immersed in the liquid phase, all the incident light rays brought to it by the bundle of optical fibers will penetrate into the liquefied gas and no light signal will appear on the observation face of the bundle of fibers , where we will only distinguish a dark spot
• - when the diopter will no longer be in the liquid phase, but there will still be gas in the phase liquid in the tank, the incident light rays will be reflected by the face or faces of the transparent body in contact with the gas phase, but not the rays which will meet the liquid phase meniscus formed in the corners of the transparent body; the observer will therefore note the appearance of a light signal of a determined shape corresponding to that of the transparent body, surrounded by one or dark zone (s), corresponding to the liquid meniscus (s);
• - when the tank will contain practically no more liquefied gas, but essentially a gaseous phase, the dark areas surrounding the light signal will disappear and will be replaced by light areas thus informing the observer that it is time to fill the tank.

In FIGS. 3 to 7, the transparent body 20 in contact with a bundle of optical fibers 22 consists of a "Plexiglas" cylinder, provided in the center of its base surface with a first dioptric element 24 of conical shape and angle at the top 90 °. It also includes a second annular dioptric element 26 of triangular section and 90 ° apex angle. The diameter of the transparent body 20 and the height of the conical dioptric element 24 are a function of the dimension of the signal which it is desired to observe. The height to be given to the second annular dioptric element 26 will depend on the nature of the transparent material constituting the body 20 and that of the gas used. The Applicant has established that, in the case of "Plexiglas" and butane, a height of 0.2 mm makes it possible, as shown in FIG. 4, to obtain two menisci 23 and 25 completely covering the dioptric element 24.

Thus when the transparent body 20 is completely immersed in the liquid gas 31 of the reservoir 30 (FIG. 5) the observation face will be completely dark (FIG. 5 '); when a little liquid gas remains (figure 6), the observation face will present a round central light (Figure 6 ') and, finally, when there is no longer any liquid gas in the reservoir 30 (Figure 7) there will appear a light signal 31 corresponding to a total reflection of the light rays on the element diopter 26 (Figure 7 '). This signal will indicate to the user that his lighter must be filled.

Figures 8 and 9 show transparent bodies 29 provided with dioptric elements of different shapes.

In the case of FIG. 8, the dioptric element 30 has the shape of a cross, while, in FIG. 9, it reproduces, upside down, the letters of the word FIN, which will thus appear to the observer as a signal of _the impending end of gas.

The invention therefore provides a simple and easy to implement means for determining the imminence of the exhaustion of gas from a li ^q uefied gas tank, which applies, moreover, particularly well to a gas lighter rechargeable liquefied, in order to signal to a user the advisability of refilling its tank with liquefied gas.

Claims (8)

1.- Device for detecting the impending exhaustion of gas in a liquefied gas tank, comprising a bundle of optical fibers (22), one end of which constitutes an observation face, is visible from the outside of the reservoir, and the other end of which, disposed inside the reservoir, is in optical contact with a flat face of a transparent element (20) comprising, on its opposite face, at least one dioptric element (24), the side walls of which form an angle, preferably obtuse, with the said face and the dimensions of which are such that it is capable, as long as there is liquid gas in the reservoir, of being covered, substantially in its entirety, by a meniscus formed of a condensate of liquid gas, which thus avoids any total reflection on said face, of the rays conveyed by the bundle of fibers. 2. A detection device according to claim 1, characterized in that the transparent element (20) comprises at least one second dioptric element (24) of sufficiently large dimensions so that the dimensions of the above meniscus are negligible compared to its own dimensions . 3.- Device according to claim 1, characterized in that the cross section of said dioptric element perpendicular to the plane of the above flat face (20) is in the form of an isosceles triangle with an angle at the top 90 °. 4. A detection device according to claim 3, characterized in that the dioptric element (24) is cone-shaped. 5. A detection device according to claim 3, characterized in that the dioptric element (26) has the shape of a crown. 6. A detection device according to claim 3, characterized in that the dioptric element has the shape of a cross (30). 7. A detection device according to claim 3, characterized in that the dioptric element (32) has the form of one or more alpha-numeric signs. 8.- Refillable gas lighter equipped with a device according to one of the preceding claims.

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